In women, one function most adversely affected by the age-related decrease in ovary reserve is decreased fecundity. The basis for this age-related change is the failure of dominant follicles to release eggs that can undergo normal embryonic development. The current thinking is that increased FSH action is involved in the mechanisms underlying decreased fecundity in women after 36 years of age. This grant represents an exciting advance in understanding the mechanisms of FSH action. Using the rat model, we have recently discovered that the oocyte is essential for estrogen activity in enhancing FSH action in granulosa cells. We have also found that the synergistic action of estrogen and oocytes occurs at a site downstream of the FSH receptor and upstream of adenylate cyclase. Further studies have provided the first evidence for a functional G protein-coupled receptor kinase (GRK)/?-arrestin system present in granulosa cells. Moreover, we demonstrate that GRK-6 is selectively suppressed by estrogen only in the presence of oocytes, suggesting that estrogen and oocytes synergistically enhance FSH action by preventing GRK-6/?-arrestin-mediated biological actions including desensitization of G protein signaling and activation of mitogen-activated protein kinase signal transduction induced by FSH. In this R21 grant proposal, we will elucidate the molecular mechanisms by which the oocyte plays an obligatory role in mediating estrogen action on the FSH sensitivity of granulosa cells. In Aim 1, we will test our hypothesis that the GRK-6/?-arrestin system is involved in the mechanism by which estrogen-oocyte co-treatment enhances FSH action. We will also provide the first comprehensive analysis of the ovarian GRK/?-arrestin system, which has been implicated in the mediation of the FSH receptor activity. In Aim 2, we will dissect the communication network between the oocyte and granulosa cell that is required for estrogen action and explore how oocytes and granulosa cells communicate in order for estrogen to stimulate FSH action. Moreover, we will identify the factor(s) that acts in the communication network between oocytes and granulosa cells to augment FSH action in the presence of estrogen, using proteomics and GeneChip. microarray analyses. The proposed project should provide a novel conceptual framework for understanding the molecular and cellular mechanisms of estrogen action in mammalian ovaries by introducing the GRK/?-arrestin system into the ovarian physiology and may lead a breakthrough in developing pharmacological regimens for treating ovarian dysfunctions, particularly in aging women. PUBLIC HEALTH RELEVANCE: Follicle-stimulating hormone (FSH) is an essential hormone for the ovarian function that includes follicle development and ovulation. We have recently discovered that estrogen enhances FSH action in follicular cells in the presence, but not absence, of oocytes. The proposed studies aim to elucidate the molecular and cellular mechanisms of this finding, which may lead to develop pharmaceutical regimens for treating ovarian dysfunctions, particularly in aging women.